Congestive heart failure (“heart failure”) is a public health concern with a significant economic impact. Subjects with congestive heart failure can require frequent hospitalization or treatment. Hospitalization or treatment for heart failure can include administration of a diuretic drug to a subject to help the subject expel excess fluid, and to thereby relieve some symptoms of congestive heart failure. A decrease in fluid, such as in a subject's thoracic region, can result in an increase in a subject's thoracic impedance or an increase in the subject's average respiratory tidal volume.
Some subjects with congestive heart failure can use wearable or implantable medical devices (IMDs) to treat heart failure and to alleviate symptoms of heart failure. Some examples of IMDs include cardiac function management (CFM) devices such as pacemakers, cardioverter defibrillators (ICDs), cardiac resynchronization devices, neural stimulation devices, cardiac monitoring devices, and devices that include a combination of multiple such capabilities, among other devices. Some devices include one or more sensors to monitor a subject's physiologic status. An IMD can be configured to evaluate a subject's health status using physiologic information received from the sensors. For example, a subject's health status can be evaluated using information from one or more of a thoracic impedance sensor or an accelerometer.
Various techniques can be used to store information in an IMD or to transmit information stored by an IMD to another device. For example, Sarkar et al., in U.S. Patent Application Publication No. US2012/0253207 entitled “Heart Failure Monitoring,” refers generally to an IMD that can be configured to transmit higher resolution diagnostic information to a clinician or external device during a hospitalization period, and can be configured to transmit lower resolution diagnostic information during a post-hospitalization period.